Power management in multi-stream audio/video devices

FIELD OF THE INVENTION

The present invention relates generally to power saving techniques in electronic circuits, and more particularly to power reduction methods suited for digital devices that are operable to process multi-stream content.

BACKGROUND OF THE INVENTION

Power consumption is a critical design constraint in many electronic devices. This is especially true of mobile devices that are usually operated using supplied DC power. Such electronic devices often contain integrated circuits that process information digitally and consume appreciable amounts of power during operation. Most dynamic power consumption in portable electronic devices such as video players occurs when their digital circuitry is actively switching, such as when decoding compressed video data to display motion video to interconnected displays.

Numerous formats suitable for organizing digital data for easy storage and convenient playback exist. In particular, digital video may be distributed using storage formats such as those used in the popular DVD format or newer, higher resolution formats such as Blu-ray. They may alternatively be streamed over a data network. Compressed video formats employed in DVDs, which are still widely available, store video in standard definition (SD) resolution. However, the newer formats which are becoming increasingly popular and are being incorporated into current and the next generation of consumer electronic devices, encode video in high definition (HD) resolution.

For example, Blu-ray supports a high definition primary video stream, a secondary video stream, two independent HD graphics streams, several audio tracks, and a background stream. These streams are used to provide improved menu interfaces, subtitles and other features that enhance user experience.

However, the improved quality and feature set listed above necessitate encoding substantial additional digital data onto a Blu-ray disc (BD). Decoding BD content would therefore require extra decoding and processing steps by decoder hardware in order to display the encoded HD video and audio content, and to provide additional features and improvements. Unfortunately, this would entail increased power consumption by the decoder hardware during playback.

Conventional power reduction techniques often emphasize optimizations at the physical circuit level, such as using lower frequency clock signal inputs, shutting down portions of a digital circuit, or reducing the supply voltage, in order to conserve power. Such techniques therefore treat many types of circuits including video decoders, generic microprocessors, memory controllers and others in essentially the same fashion and although each circuit may be geared towards different purposes.

Conventional techniques may thus fail to deliver adequate power reduction since they do not take particular application contexts into account. Accordingly, there is a need for improved power conservation techniques suitable for digital audio/video devices such as BD players.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there is provided a method of processing a plurality of digital audio/video streams at an audio/video device to output audio/video in one of at least two power consumption modes. In a first normal power consumption mode, the method involves digitally processing at least a first and second one of the digital streams; and detecting a desired reduced power consumption mode for operating the device. In response to detecting a reduced power consumption mode, the method involves selecting a modified manner to digitally process the second one of the digital streams, digitally processing the first one the streams in the same manner as in normal mode, and digitally processing the second one of the digital streams in the selected modified manner in order to reduce dynamic power consumed by the device as a result of digitally processing the second stream.

In accordance with another aspect of the present invention, there is provided a method of operating a computing device to playback of a video stream and an audio stream from a source. The method includes decoding video frames from the video stream. In a normal power consumption mode, the method involves compositing corresponding ones of the video frames from the video stream with other applications in the device to form output images and displaying the output images onto a display while decoding and outputting the audio stream. In response to detecting a reduced power consumption mode, the method involves maximizing and outputting the video frames in full screen exclusive mode, so as to block the other applications from presenting on the display, while decoding and outputting the audio stream in the same manner as in the normal mode.

In accordance with another aspect of the present invention, there is provided a method of operating a computing device to playback of a plurality of video streams from a source. The device includes a processing engine, memory storing processor executable instructions in communication with the engine and an output interface interconnected to a display. The method includes, in a normal power consumption mode, decoding at least a first stream and second stream, forming video frames from the second stream, and digitally processing the video frames using a first algorithm. The method also includes, in response to detecting a reduced power consumption mode, digitally processing the video frames using a second algorithm that is computationally simpler than the first algorithm, while digitally processing the first stream in the same manner as in the normal mode.

In accordance with another aspect of the present invention, there is provided a video player device operable in at least two power consumption modes, for digitally processing and outputting a plurality of audio/video streams. The device includes a drive for reading a medium containing the streams; and a processing engine in communication with memory and the drive. The memory contains processor executable instructions for decoding and processing the streams. In a first normal power consumption mode, the device digitally processes at least a first and a second one of the plurality of streams to form and output audio/video content; and in response to detecting a desired second reduced power consumption mode, the device selects a modified manner to digitally process the second one of the streams and digitally processes the second one of the streams in the modified manner, in order to reduce dynamic power consumed by the device as a result of digitally processing the second one of the plurality of streams, while digitally processing the first one of the plurality of streams in the same manner as in the normal power consumption mode.

Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures which illustrate by way of example only, embodiments of the present invention,

<figref idref="DRAWINGS">FIG. 1</figref> is a schematic block diagram of a digital video player, interconnected to a speaker and a display;

<figref idref="DRAWINGS">FIG. 2</figref> is a flowchart generally depicting a method of decoding and displaying multi-stream audio/video using the device of <figref idref="DRAWINGS">FIG. 1</figref>, in an exemplary embodiment of present invention;

<figref idref="DRAWINGS">FIG. 3</figref> is a flowchart depicting a particular method of decoding and displaying multi-stream audio/video using the device of <figref idref="DRAWINGS">FIG. 1</figref>, in an exemplary embodiment of present invention;

<figref idref="DRAWINGS">FIG. 4</figref> is a flowchart that depicts the actions of an exemplary processing circuit, in which main frames are decoded and displayed at a full frame rate, while auxiliary frame rates are composited at a reduced frame, rate when in reduced power consumption mode;

<figref idref="DRAWINGS">FIG. 5</figref> is a schematic depiction of selective composition of frames of an auxiliary stream with corresponding frames of a main video stream;

<figref idref="DRAWINGS">FIG. 6</figref> is a flowchart of the actions of an exemplary device processing multi-stream video, while a menu is being displayed;

<figref idref="DRAWINGS">FIG. 7</figref> is a flowchart of the actions of an exemplary device when processing multi-stream audio;

<figref idref="DRAWINGS">FIG. 8</figref> is a flowchart of the actions of an exemplary device decoding video for display using a video application window on a computer;

<figref idref="DRAWINGS">FIG. 9</figref> is a flowchart of the actions of an exemplary device processing multi-stream video, depicting the use of simpler processing algorithms when in reduced power consumption mode, to conserve power; and

<figref idref="DRAWINGS">FIG. 10</figref> is a flowchart depicting exemplary steps performed by an exemplary device having at least two lower power consumption modes, to decode and display multi-stream audio/video.

DETAILED DESCRIPTION

Devices that process and present multi stream video and audio data are becoming common place. Similarly, devices that support so-called high definition resolution video (1920×1080 or 1280×720 pixels) are emerging. In the future even higher resolutions may be common place. Currently, Blu-ray standard compliant players support a main or primary video stream along with auxiliary streams including a secondary video stream, a background stream, a presentation graphics (PG) stream and an interactive graphics (IG) stream. In Blu-ray, the primary video stream is of a high definition resolution (1920×1080). Two independent graphics streams (i.e., the IG and the PG streams) are used to provide menus, buttons, subtitles, animation and the like. In addition, auxiliary streams such as the secondary video stream in Blu-ray may be used for director's commentary. Similarly, Blu-ray supports multiple audio streams, which may provide audio in varying audio formats, resolutions, channels, languages, and content. Other standards that support multiple audio and video streams include the integrated services digital broadcasting standards (ISDB) supported in Japan and elsewhere.

High definition video and associated audio may be stored on an optical Blu-ray disc (BD) in compliance with one of several formats such as the BD-recordable (BD-RE), BD-pre-recorded or BD-read-only-memory (BD-ROM) and BD-write-once (BD-R) formats. BD-ROMs may often be used to distribute movies, music videos and the like in high definition video and surround-sound audio and including subtitles and other features.

A compliant video player, in turn, can decode each stream of video/audio data and provide decoded video/audio signals to interconnected output devices such as a display, an audio amplifier or speaker, or the like.

More specifics about Blu-ray may be found in Blu-ray Disc Format Specifications including for example, the Blu-ray Disc Read-Only (ROM) Format Version 2.0 defined in May of 2006.

<figref idref="DRAWINGS">FIG. 1</figref> illustrates a simplified block diagram of a video player device <b>100</b>, exemplary of an embodiment of the present invention. Device <b>100</b> includes a processing engine <b>104</b> that includes a host processor <b>106</b>, a memory interface circuit <b>120</b>, and a video and graphics processor <b>114</b>. Video and graphics processor <b>114</b> may have its own local memory <b>124</b>. Processing engine <b>104</b> may further include an audio processor <b>126</b>, and an input-output (I/O) interface circuit <b>122</b>. Memory interface circuit <b>120</b> may provide processing engine <b>104</b> with a control interface to computer readable memory <b>108</b>. I/O interface circuit <b>122</b> may provide a number of standard I/O interfaces to processing engine <b>104</b>, including for example peripheral, video and audio interfaces, such as HDMI, S-Video, component video, DisplayPort™ interfaces. SATA, or USB interfaces, multichannel audio interfaces, and the like. A multi-stream video/audio source <b>102</b> may be in communication with processing engine <b>104</b> and audio processor <b>126</b> through interface circuit <b>122</b>. Processing engine <b>104</b> may also be interconnected with computer readable memory <b>108</b> by way of an internal memory interface circuit (not shown). A speaker <b>116</b> may be attached to audio processor <b>126</b> through I/O interface circuit <b>122</b> and be used to output video and audio.

Multi-stream video/audio source <b>102</b> may be a memory with suitable reader—such as an optical BD and drive; it may be a cable or terrestrial television tuner; or it may simply be logic capable of downloading or streaming multi-stream video/audio from a communications network.

Suitable software causing device <b>100</b> to decode audio/video and operate in manners exemplary of embodiments of the present invention may be stored in system memory <b>108</b>. Processor executable instructions specific to host processor <b>106</b>, video and graphics processor <b>114</b> and audio processor <b>126</b> may be loaded into memory <b>108</b>, and read by processing engine <b>104</b>. The instructions may be used by video and graphics processor <b>114</b> to carry out many image processing functions including video decoding, scaling, de-interlacing, image composition, chroma up-sampling and the like. Audio processor <b>126</b> may similarly perform audio decoding, audio encoding, re-sampling, mixing and the like. Host processor <b>106</b> may be used to manage device <b>100</b>, and assist in some decoding phases such as de-multiplexing.

Display <b>118</b> may be an LCD panel, or the like. A display interface such as HDMI, VGA, DisplayPort, DVI or the like (not shown) may interconnect display <b>118</b> to processing engine <b>104</b>.

In some embodiments device <b>100</b> may be a dedicated video player, such as a BD player capable of reading encoded digital video distributed using a BD; a high definition media player; a portable electronic device, such as cellular telephone, a personal digital assistant, a video game, or the like. In such embodiments, some components of <figref idref="DRAWINGS">FIG. 1</figref> may be omitted or replaced with other similar functional blocks, formed in software, as firmware, hardware otherwise, in manners understood by those of ordinary skill.

In an exemplary embodiment, device <b>100</b> may, for example, take the form of a general purpose personal computer, such as a laptop computer or workstation, acting as a BD player. In such an embodiment, host processor <b>106</b> may be a central processing unit (CPU) with an AMD x86 based architecture. Source <b>102</b> may be an optical disc drive, loaded with a suitable storage medium such as a BD. Interface circuit <b>120</b> may be high speed peripheral interface—such as “the north bridge”, while I/O interface circuit <b>122</b> may be a low speed peripheral interface—commonly called “the south bridge”. Source <b>102</b> may be interconnected to I/O interface circuit <b>122</b> by way of a serial advanced technology attachment (SATA) bus or a similar suitable bus. Video and graphics processor <b>114</b> may be a graphics processing unit (GPU) formed on a Peripheral Component Interconnect Express (PCIe) graphics card or an integrated graphics processor (IGP) within processing engine <b>104</b>.

In operation, a suitable source of audio video content provides multiple streams to device <b>100</b>. In the depicted explanatory embodiment, multiple streams may be provided by stream source <b>102</b> in the form of an optical disc drive having a digital medium (e.g., BD) containing multi-stream audiovisual content loaded thereon. The optical drive may be capable of reading and transferring encoded data from the disc to processing engine <b>104</b> in device <b>100</b>.

Each image constructed from the contents of a BD by device <b>100</b> may include video contained in the main (primary) video stream, and auxiliary streams such as a secondary video stream, the IG stream, the PG stream and a background stream. The primary and secondary video streams may, for example, be encoded in one of an MPEG-2, MPEG-4 AVC (or H.264) and SMPTE VC-1 compliant formats. The secondary video stream may be used for picture in picture (PiP) video. The PG stream may include encoded graphics objects, color look-up tables (GLUT) and other encoded data.

In normal operation, processing engine <b>104</b> in device <b>100</b> may decode the main video stream into main video frames (e.g., primary video frames), and each of the auxiliary streams into auxiliary frames (e.g., graphics overlay images or PiP secondary frames) containing corresponding images which may be combined (or composited) with the main frame to form final images for display, in accordance with Blu-ray Disc Format Specifications.

The IG stream may be used to provide menu graphic objects for commands associated with interactive displays during a movie presentation. The PG stream may be used to provide information required for non-interactive overlays that are supplemental to the primary video content such as for example, subtitles and animated graphics. In Blu-ray, the images in the IG and PG streams are independent of each other and also of the primary video stream. Both IG and PG streams may also include various wipes, fades and scroll effects. Composition segments within the IG and PG streams, indicate graphics objects to be used for a graphics display, and may define cropping transforms to be applied when compositing graphics objects. Composition segments also indicate a palette to be used for graphics displays. Effects such as wipes, scrolls and cuts can be realized by providing multiple compositions segments which change cropping areas of graphics objects.

Images from each stream are decoded, processed and subsequently composited together into output frames for display. Compositing typically involves alpha blending of two or more images. A frame from the main video stream may for example be overlaid with images decoded from the graphics streams. Final display frames or images are provided to display <b>118</b>. Images to be composited may be mixtures of high definition resolution and standard definition. For interactive or feature-rich presentations, the display image may be formed from the superposition of corresponding frames from of the multiple streams.

To reduce power consumption in exemplary embodiments of the present invention, decoding methods may take into consideration, the data organization of audio/video streams as received from source <b>102</b>. As will become apparent, different decoding, processing and/or compositing techniques may be utilized for at least one of the multiple streams, based on whether the device is operating in a normal power consumption mode, or in a reduced power consumption mode.

That is, all streams may be decoded, and digitally processed and displayed in a conventional manner when device <b>100</b> is operating in its normal power consumption mode. While in a reduced power consumption mode, some of the auxiliary streams may be digitally processed in a modified manner to reduce power consumption. That is, auxiliary streams may not be decoded, or may not be digitally processed, when in reduced power consumption mode. Alternatively, as will become apparent, the auxiliary streams may be partially decoded, or digitally processed using less computationally intensive algorithms.

The auxiliary streams that may not be decoded in reduced power consumption mode are, in some embodiments, selected by commands or controls (e.g., buttons, check boxes, etc.) by way of user interface software executing on processor <b>106</b>. Additionally, the specifics of a reduced power consumption mode of device <b>100</b> may be pre-programmed by a manufacturer, or possibly set by user input. For example, a user may control via a user interface, which auxiliary streams are excluded from certain decoding and/or processing steps, or from a composition stage, when in a reduced power mode.

For example, in a BD player, a user may be particularly interested in the subtitles and hence may select to decode the presentation graphics stream while omitting the interactive graphics stream, or the background stream if any, when in a reduced power consumption mode.

Thus, in one exemplary embodiment of the present invention, in a reduced power consumption mode only video frames from the primary stream may be used to form display output image on display <b>118</b> while images decoded from the auxiliary streams are inhibited or suppressed. That is, the encoded auxiliary streams, may not be read and/or decoded from the medium (e.g., BD) at all, while each frame of the main (e.g., primary) video stream is read and decoded to form display image and displayed on to display <b>118</b>. As may be appreciated, this may significantly reduce the computational demands on GPU <b>114</b>, and processor <b>106</b> which in turn reduces power consumption in device <b>100</b>.

Transition between operation of device <b>100</b> in its normal power consumption mode and its reduced power mode may be effected in numerous ways. For example, the transition may be triggered by manual user intervention (e.g. a switch, button or the like), or in response to sensing limited available power. In one embodiment, device <b>100</b> may be a portable, battery operated device such as a laptop computer. Processor <b>106</b> may monitor the battery level of device <b>100</b>, and when the battery level is below a certain threshold, may place device <b>100</b> in a reduced power consumption mode. Alternately, processor <b>106</b> may monitor the power source, and transition device <b>100</b> to its reduced power consumption mode upon detecting device <b>100</b> is no longer interconnected with an AC source, such as the mains. Alternatively, processor <b>106</b> may compare the time remaining on currently playing content (e.g. a movie), with available playing time left at a normal power consumption rate given its current battery level. If processor <b>106</b> determines that device <b>100</b> would not be able to complete playback of the current track or movie presentation at its current normal rate of power consumption, processor <b>106</b> may place device <b>100</b> in a low power consumption mode to allow completion of the presentation.

When in reduced power consumption mode, processing engine <b>104</b> (or GPU <b>114</b>) may only render frames from the primary video stream (main video stream) from stream source <b>102</b>. Frames from auxiliary streams (e.g., graphics overlays) would thus not be composited for display. Of course, in normal power consumption mode, corresponding images from each stream may be combined and displayed.

<figref idref="DRAWINGS">FIG. 2</figref> illustrates a flowchart depicting steps taken by exemplary device <b>100</b> to decode and display frames from a multi-stream audio/video source (e.g., stream source <b>102</b>) in an exemplary embodiment of the present invention. Of course, steps in <figref idref="DRAWINGS">FIG. 2</figref> need only be performed in the presence of multiple streams. First, device <b>100</b> determines the power consumption mode (S<b>202</b>) based on for example, battery level. If device <b>100</b> determines that it should operate in a normal power consumption mode (S<b>204</b>) then it may decode and digitally process at least two streams (typically all active streams) using normal power consumption processing (S<b>206</b>). It may then output the final audio/video content (S<b>208</b>) formed using normal power consumption mode processing.

On the other hand, in response to detecting a desired reduced power consumption mode in S<b>204</b>, device <b>100</b> may decode and digitally process, at least one stream in normal power consumption mode; and at least one other stream in a modified manner—i.e., using reduced power consumption mode processing (S<b>210</b>). It may then form and output final audiovisual data (S<b>212</b>) formed using reduced power consumption mode processing. Final images may be output (S<b>214</b>) by device <b>100</b>, and these steps may be repeated (S<b>216</b>) until all of the input data is processed.

In one specific embodiment, video device <b>100</b> may operate to playback of a plurality of audio/video streams from a source (e.g., BD). The audio/video streams typically include at least a first stream (e.g., the primary video stream) and a second stream (e.g., the secondary video stream). As depicted in <figref idref="DRAWINGS">FIG. 3</figref>, during device operation, video frames from the primary stream are decoded. In normal power consumption mode, video frames or graphics images from the secondary stream may be decoded and combined with corresponding video frames from the first video stream to form output images. The secondary stream may for example be presented as a picture-in-picture video. Composited output images are then displayed on a display.

In response to detecting a reduced power consumption mode however, as depicted in <figref idref="DRAWINGS">FIG. 3</figref>, device <b>100</b> may only decode (S<b>302</b>) and form video frames (S<b>304</b>) from the primary stream in a modified manner, without combining them with video images from the secondary stream. In reduced power consumption mode, decoding and processing of the secondary stream may thus be inhibited.

In another exemplary embodiment, device <b>100</b> or its processing engine <b>104</b> may decode, process, and display some input streams at different rates. For example, in normal power consumption mode, processing engine <b>104</b> may decode and composite all corresponding images from each of the input video streams, and display the composited frames. In a reduced power consumption mode however, as depicted in <figref idref="DRAWINGS">FIG. 4</figref>, device <b>100</b> may decode all images from a first stream (S<b>702</b>) and but only a subset of images from a second (e.g., overlay) stream (S<b>704</b>) received from a stream source (e.g., stream source <b>102</b>). Processing engine <b>104</b> may thus composite the subset of images decoded from the second stream onto corresponding images from the first stream (S<b>706</b>) and output the composited images (S<b>708</b>).

In a normal power consumption mode, processing engine <b>104</b> may composite and display decoded images from both the first (e.g., primary) video stream and the auxiliary (e.g., presentation graphics) stream at the full frame rate (e.g., 30 Hz). In a reduced power consumption mode however, processing engine <b>104</b> may decode every other encoded auxiliary image, and composite each decoded auxiliary image with one or more corresponding main (primary) frames. Thus, processing engine <b>104</b> may display one primary video frame composited with an auxiliary image (e.g., presentation graphics image), followed by another primary video frame composited with the same auxiliary image.

<figref idref="DRAWINGS">FIG. 5</figref> schematically illustrates one such composition of decoded images from multiple video streams. As depicted, the main or primary stream includes frames <b>602</b>-<b>1</b>, <b>602</b>-<b>2</b>, <b>602</b>-<b>3</b>, . . . <b>602</b>-N (individually and collectively frames <b>602</b>), while an auxiliary stream (e.g., the presentation graphics stream) includes corresponding images <b>604</b>-<b>1</b>, <b>604</b>-<b>2</b>, <b>604</b>-<b>3</b>, . . . <b>604</b>-N (individually and collectively images <b>604</b>). In normal power consumption mode, each image in the secondary stream may be decoded and composited with a corresponding frame from the primary stream and presented. However, in a reduced power consumption mode, every other image from the secondary stream may be decoded. That is, only image <b>604</b>-<b>1</b>, <b>604</b>-<b>2</b> . . . <b>604</b>-N may be decoded. After decoding, composition is performed as depicted to form output frames <b>606</b>-<b>1</b>, <b>606</b>-<b>2</b>, <b>606</b>-<b>3</b> . . . <b>606</b>-N (individually and collectively output frames <b>606</b>). Output frame <b>606</b>-<b>1</b> is formed by compositing corresponding main frame <b>602</b>-<b>1</b> and secondary stream image <b>604</b>-<b>1</b>. However, output frame <b>606</b>-<b>2</b> is formed by compositing frame <b>602</b>-<b>2</b> and image <b>604</b>-<b>1</b> (as image <b>604</b>-<b>2</b> is not decoded in a reduced power consumption mode). Output frame <b>606</b>-<b>3</b> (like frame <b>606</b>-<b>1</b>) is formed by compositing corresponding primary frame <b>602</b>-<b>3</b> and image <b>604</b>-<b>3</b> while output frame <b>606</b>-<b>4</b> is formed by compositing frame <b>602</b>-<b>4</b> and image <b>604</b>-<b>3</b> (as image <b>604</b>-<b>4</b> is not decoded). Finally output frame <b>606</b>-N is formed by compositing frame <b>602</b>-N and image <b>604</b>-N.

In yet another variation, processing engine <b>104</b> may pause displaying video from one stream altogether, whenever an interactive graphics frame (e.g., menu) is displayed. As depicted <figref idref="DRAWINGS">FIG. 6</figref>, device <b>100</b> (or specifically processing engine <b>104</b>) may decode a first interactive graphics (IG) stream (for menus) (S<b>904</b>) and a second video stream to display video frames (S<b>902</b>). Device <b>100</b> may receive a user input to display a menu (S<b>906</b>). In normal power consumption mode, a decoded interactive graphics image from the first stream may be used to present a menu for interaction with a viewer, while the video stream continues to be decoded and displayed in the background. However, upon determining a reduced power consumption mode (S<b>204</b>), the second (video) stream may be paused, and menus or buttons, the interactive graphics image may be displayed over a paused (i.e., static) current video frame (S<b>908</b>, S<b>910</b>). That is, in a reduced power consumption mode, the video stream would not be playing while the menu is displayed and consequently power consumption can be reduced. In either power consumption case, user command input via the displayed menu (i.e., interactive graphics stream) may be received and processed (S<b>912</b>). The process may be repeated until the streams are decoded and displayed. In a variation of this embodiment, device <b>100</b> may stop (rather than pause) the playback of the primary video entirely, so that composition with the primary video frame is not required when presenting a menu in a reduced power consumption mode.

In another embodiment, audio decoding and outputting may be selectively performed as described below using the flowchart depicted in <figref idref="DRAWINGS">FIG. 7</figref> to conserve power. An audio source (e.g., a BD) may present several audio tracks including for example, PCM encoded audio, Dolby Digital (AC-3) encoded surround sound audio, DTS encoded surround sound audio and the like. PCM encoded audio may have up to 8 channels encoded at a sample rate of 48 KHz or 96 KHz, with 16, 20, or 24 bits per sample. To conserver power, processing engine <b>104</b> may decode only a subset of the available audio data; or if multiple audio tracks are available, decode a lower quality audio track requiring less power to process. For example, processing engine <b>104</b> may decode and output a first track in one format (e.g., DTS) when in normal consumption mode. However, to conserve power, processing engine <b>104</b> may select a lower quality track (S<b>1002</b>) in a second format (e.g., PCM encoded audio) and decode (S<b>1004</b>) and form an audio output (S<b>1004</b>) upon detecting a reduced power consumption mode.

In addition, only a subset of the channels of a PCM encoded audio (e.g., 4 out of 8 channels) may be decoded for output in order to conserve power. In addition PCM audio encoded at a rate of 96 KHz, may be sub-sampled down to 48 KHz prior to output to conserve power.

In some embodiments, the first and second streams being decoded by device <b>100</b> may both be audio streams. For example, in a Blu-ray disc, device <b>100</b> may present both the audio track of a primary video, and the director's commentary in a secondary audio and video, together with the primary audio track. The director's commentary may of course be suppressed, or otherwise processed in a modified manner to conserve power, as needed.

In another embodiment, multichannel audio, such as Dolby Digital or DTS encoded surround sound audio may be decoded for playback on fewer speakers than the number of encoded audio channels. Here, processing engine <b>104</b>, may down-mix the multichannel audio input (e.g. six channels for 5.1 surround sound) into fewer channels corresponding to the number of speakers desired (e.g., two speakers). Down-mixing may be used by processing engine <b>104</b>, when in normal power consumption mode. However, in a reduced power consumption mode, processing engine <b>104</b> may simply select and output the desired number of channels (e.g., front left and front right channels only) to interconnected speakers to reduce computation and hence power consumption. Of course various down-mixing options are available to output 5.1, 7.1 or 10.1 encoded multichannel sources to 2.1 or 2 channel output systems.

In yet another embodiment of the present invention, device <b>100</b>, in the form of a computing device such as a laptop receiving an audio/video stream, may force a full screen video output on connected display <b>118</b>, in response to reduced power mode detection. This allows processing engine <b>104</b> to avoid compositing the video player application with other applications and/or the desktop background on display <b>118</b>, thereby helping to conserve power consumption. As depicted in <figref idref="DRAWINGS">FIG. 8</figref>, upon detection of a reduced power consumption mode (S<b>1102</b>), device <b>100</b> may decode a video stream (S<b>1102</b>) for display using a video application window on a computer (e.g., laptop). The application window may be maximized (S<b>1104</b>) to display the window without any composition with other windows or the desktop. The application with a maximized window may have exclusive access to the display screen, so that no composition is taking place in the background. For example, the DirectX application programming interface (API) includes options that provide full screen exclusive mode access to the frame buffer to a client application in a computer. Thus in step S<b>1104</b> the video application may utilize full screen exclusive mode access to the frame buffer, to present maximized images while blocking other application from presenting images for composition or display. Of course, in normal power consumption mode, the video application window may be composited with other application windows and the composited output image may be displayed. Processing engine <b>104</b> may continue to decode and output an audio stream in the same manner in both normal and reduced power consumption modes.

In yet another embodiment, processing engine <b>104</b> may perform various audio/video processing tasks using computationally more demanding higher quality algorithms and parameters on at least a first and second audio/video streams during normal power consumption mode. Upon detecting a reduced power consumption mode however, processing engine <b>104</b> may utilize simpler algorithms and/or parameters which are computationally simpler, but may lead to a lower quality output on the second video stream. As depicted in flowchart of <figref idref="DRAWINGS">FIG. 9</figref>, device <b>100</b> may for example, decode and scale frames of the second stream, depending on the power consumption mode. Upon detection of a reduced power consumption mode (S<b>204</b>), lower order filtering or a simple scaling algorithm (e.g., nearest neighbor interpolation) may be used (S<b>1208</b>) after decoding the second stream (S<b>1206</b>). However in a normal mode, higher order filters such as a more complex interpolation (e.g., bicubic) or may be used, (S<b>1204</b>) for scaling and other processing, after decoding (S<b>1202</b>) the second stream. In both power consumption modes, the first stream may be digitally processed in the same manner, using higher order filters, more complex interpolation, or other more complex higher quality algorithms.

In addition, in one variation of the above embodiment, a computationally complex algorithm such as inverse telecine may be used for frame rate conversion in normal power consumption mode. However computationally simpler algorithms may be used when in reduced power consumption mode to digitally process the second stream. For example, inverse telecine operations on the second stream may be dropped altogether when in a reduced power consumption mode.

In these embodiments IG and/or PG streams may be treated as the first stream—in a conventional manner.

In other embodiments, multiple streams may be multiplexed and received over a data network, over a cable television network, over a satellite network, as part of a terrestrial television transmission, from a disk drive, or from some other data source.

Further, one or more of de-noise, scaling, frame rate conversion, gamma correction, or de-interlacing operations may be operated with lower quality parameters or using simpler algorithm on one of the two streams to reduce computation and thus to ultimately limit power consumption. For example, in a reduced power consumption mode, inverse telecine operations may be discarded during frame rate conversion.

In a variation of the above embodiment, device <b>100</b> may decode a main video stream (e.g., primary stream in BD) and only some of the auxiliary streams (e.g., only IG or only PG in BD) when in a reduced power consumption mode, to fine tune power consumption/conservation. Specifically, device <b>100</b> which may be a battery operated laptop for example, may have two reduced power consumption modes in which the first reduced power consumption mode is entered when the energy level of the power source (e.g. battery level) P is below a first threshold ε₁but above a second threshold ε₂which is lower than the first threshold. That is, the first reduced power consumption mode is entered when ε₂&lt;P&lt;ε₁. Device <b>100</b> may enter a second reduced power consumption mode when its battery level P has fallen to or below the second threshold (i.e., when P≦ε₂).

As shown in steps S<b>400</b> in <figref idref="DRAWINGS">FIG. 10</figref>, in this embodiment, device <b>100</b> always decodes the main or primary video stream (S<b>402</b>). If the battery level P is below the second threshold ε₂, then device <b>100</b> is in a second power consumption mode and only the main video frame is displayed (S<b>412</b>).

However, if the battery level P is above second threshold ε₂but below the first threshold ε₁(S<b>406</b>),—i.e., ε₂&lt;P&lt;ε₁—then device <b>100</b> is in its first reduced power consumption mode, and decodes one auxiliary stream (S<b>408</b>) (e.g., the IG stream).

If the battery level P is above the first threshold ε₁, (that is, P&gt;ε₁) then device <b>100</b> is in a normal power consumption mode, and decodes more of its auxiliary streams (e.g., decodes both the interactive graphics stream and the presentation graphics stream) in addition to the main video stream; and composites the decoded main and interactive images together to form and display the final image (S<b>410</b>).

In normal power consumption mode and the first reduced power consumption mode, the decoded images are combined or composited and displayed (S<b>412</b>). In the second reduced power consumption mode, composition is not required as only the main video frame is displayed. If more video and graphics stream data remain (S<b>414</b>) the process starts again (S<b>402</b>).

It is easy to see that above embodiment may be generalized for N reduced power consumption modes corresponding to N threshold values (ε₁, ε₂, . . . ε_Nwhere ε_j&lt;ε_j+1for 1≦j&lt;N) associated with the power level in device <b>100</b>, which may be used to provide flexible power management within device <b>100</b>. For example, the secondary video stream in Blu-ray discs may be easily accommodated in this scheme.

Of further interest, one or more thresholds c may be computed dynamically—for example, in dependence on the energy required to decode one or more streams to be listened to by a user for the remaining time of a particular stream (e.g. for the remaining time of a feature or movie, as for example carried by the primary stream) being viewed or listened to. Remaining time may be extracted from the video or auxiliary stream in a conventional manner. The energy required to view or listen to the remainder of the stream may be computed as the product of the average amount of power per unit time consumed while decoding one or more streams, times the remaining time. Further thresholds may be computed assuming various combinations of decoding techniques for the multiple streams—e.g. assuming fewer streams are decoded, or multiple streams are decoded in a modified manner to reduce dynamic power consumption, while allowing the stream of interest to be viewed or listened to. If a threshold ε_FEATUREis determined for which the entire or remainder of the feature can be viewed or listened to for an available energy level P of the power source (e.g. battery), streams may be decoded using the associated combination of decoding techniques for the streams. In this way, a lower power mode may be assumed in order to ensure that a particular stream may be decoded (i.e. viewed/listened to) to completion using available power.

Of course, the above described embodiments are intended to be illustrative only and in no way limiting. The described embodiments of carrying out the invention are susceptible to many modifications of form, arrangement of parts, details and order of operation. The invention, rather, is intended to encompass all such modification within its scope, as defined by the claims.